The Effect of Bleaching Agents on the Microstructure and Surface Microhardness of Three Calcium Silicate-based Barrier Materials

The aim of this study was to evaluate the effects of exposure to sodium perborate and H2O2 on the surface characteristics of MTA Angelus, Biodentine and MTA Repair HP after 1 and 6 month time intervals.

Three calcium silicate-based cements were evaluated: MTA Angelus, Biodentine, MTA Repair HP. A total of 234 specimens were stored in Hank’s balanced salt solution (HBSS) for 1 month or 6 months in which afterwards were divided into 3 groups according to bleaching agent applied: control, sodium perborate, 35% hydrogen peroxide. The microstructural changes were evaluated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The surface microhardness was also evaluated. Data were analyzed by one-way analysis of variance and Games-Howell post-hoc tests for the effect bleaching agents and hydraulic calcium silicate-based cements and t-test was for the effect of time.

Distinctive alterations with uneven depression areas, woodpecker defects and cracks were seen due to exposure to perborate and H2O2 on all evaluated cements. Exposure to H2O2 caused a decrease in Ca/Si ratio in all experimental cements. Both H2O2 and perborate significantly decreased the microhardness of all cement (P<0.05) with H2O2 having a more profound effect (P<0.01). A 6-month delay in exposure to bleaching agents significantly increased the microhardness of Biodentine compared to 1 month (P<0.001 for both bleaching agents).

Based on this in vitro study, H2O2 had more detrimental effects on MTA Angelus, Biodentine and MTA Repair HP. Sodium perborate may be a more conservative selection when considering effects on barrier materials.Keywords: Bleaching Agent; Calcium Silicate Cement; Microhardness; Mineral Trioxide Aggregate; Scanning Electron Microscopy